"The majority of incidents involve roof damage from fallen trees and branches and trees falling across powerlines, fences and driveways," the spokesman said.

People have been advised to put away or secure loose items on their property, move vehicles under cover or away from trees, and to stay clear of fallen power lines.

Sydney temperatures are expected to drop as low as 10 degrees overnight. Snow is also reportedly falling in parts of the Blue Mountains, with heavy falls at Thredbo Village.

The front is expected to move through the Hunter this evening, the Bureau of Meteorology said.

"Damaging winds with gusts of 90 to 100 km/h in the Sydney Metropolitan area are expected to ease early this evening, and at this stage are not expected to redevelop (on Sunday)," the bureau said in its updated warning. "However winds are expected to be quite strong and gusty."

Drive with care

Motorists are being warned to reduce speed and drive with caution due to a number of fallen trees and power failures, particularly across Sydney's northern suburbs.

There have been several traffic light black outs in the Castle Hill area and Dundas, where winds speeds are already reaching 90km/h. There are also electrical wires down on Ryde Road in Pymble.

Meanwhile, a fallen tree on Wakehurst Parkway at Seaforth has affected motorists in both directions.

One witness said the entire road was taken out by the tree, fortunately no one was injured as it fell.

"A few seconds more and we'd have been hit," the motorist said. "It makes you realise how people can get killed by falling trees."

Several fallen branches along the road are also slowing traffic in the area.

Windy Sunday too

Weatherzone meteorologist Gareth Dixon told Fairfax Media that Sydney was in for a rough weekend with north-westerly winds reaching gale force strength after midday Saturday and remaining strong for Sunday.

"It's going to be a gradual increase instead of a smack in the face sort of change but after lunch we're expecting winds of over 60 kilometres per hour, with damaging gusts of 90 kilometres an hour."

The dangerous winds will be the most significant feature of the incoming cold front for Sydney, unlike Canberra, Melbourne and Adelaide where the front will also bring rain.

A front combined with a strong low-pressure system hit south-eastern Australia earlier this week, bringing down trees and resulting in coastal inundation of parts of Victoria.

Cold end for a warm June

Weatherzone's Mr Dixon says rain is unlikely in Sydney with the coming front.

The city had been in the midst of its second "warm wave" this month, with maximum temperatures running about 3 degrees above the long-run average so far in June.

However the cold front knocked temperatures down from a maximum of almost 23 degrees on Saturday - about 6 degrees above average - to below 14 degrees by late afternoon. Sunday's top is forecast to reach 17 degrees and 16 degrees on Monday.

The Hunter, Illawara, South Coast, Southern and Central tablelands, Snowy Mountains and South West Slopes regions are all likely to be affected by Saturday's windy blast.

Residents in the Snowy Mountains and South West Slopes should also prepare for blizzard conditions, adding to the past week's big snow dump.

Beyond the windy weekend, maximum temperatures in Sydney should start to creep back up to about 20 degrees by midweek, with little if any rain likely before next weekend, according to the bureau's updated forecast.